fix timeline events covers series (#43780)

frontend/src/metabase/visualizations/echarts/cartesian/constants/style.ts

@@ -9,11 +9,11 @@ export const LINE_SIZE: Record<LineSize, number> = {
 export const Z_INDEXES = {
   // Note: timeline events use echarts' markline option, which has a fixed z
   // value of 5.
-  dataLabels: 3,
-  goalLine: 2,
-  trendLine: 2,
-  lineAreaSeries: 2,
-  series: 1, // Bars needs to have a lower z value than line/area series, see issue #40209
+  dataLabels: 8,
+  goalLine: 7,
+  trendLine: 7,
+  lineAreaSeries: 7,
+  series: 6, // Bars needs to have a lower z value than line/area series, see issue #40209
 };
 
 export const CHART_STYLE = {